1. Technical Field
The present invention relates to computer systems with automated tape libraries and virtual tape storage, and more particularly to computer systems emulating the Small Computer System Interface to access those virtual tape devices.
2. Description of the Related Art
In a multiserver/multiprocessor architecture, such as an IBM(copyright) Enterprise class system, it is a common practice for a storage subsystem providing one method of access, such as an ESCON(copyright) interface, to emulate or provide an additional method of access, such as the Small Computer System Interface (of SCSI) standard. This is done to allow use of the storage subsystem by Open System file servers.
In the case of a tape server using automated tape libraries, this type of additional method of access has only been partially provided. The open system file servers access the tape drives via the standard SCSI interface. However, the medium changer commands of the SCSI interface have not been, so far as is known, emulated or supported. Instead, in place of issuing standard SCSI medium changer commands, the open system file server or host would have to issue Perform Library Function commands, as found in the ESCON(copyright) interface, via a second connection to the virtual tape server subsystem. This arrangement did not fully emulate the SCSI interface of a tape library and was not easily incorporated in the Open system computer operating code or applications.
A typical prior art Open System for computers is shown in FIG. 1 having an Open System host computer 2 in the form of a conventional workstation or file server of any suitable type. Host computer 2 is attached to send Small Computer System Interface (SCSI) tape commands over a SCSI bus as indicated at 4 to a virtual tape server 6 of a tape library 8. The virtual tape server 6 performs tape drive commands received from SCSI bus 4 to logical tape drives on logical volume managed by the entire system 8.
Tape library commands, also know as medium changer commands, on the other hand, from the host workstation 2, so far as is known, have not been transferable over the SCSI bus 4 through the server 6 to the library manager 12. Instead, tape library commands have been transferred to the tape library module 12 over a separate path 10, typically through a local area network (LAN), over an RS-232 connection, or other known, conventional computer interconnection network. As has been set forth above, this technique for access to virtual data storage emulating SCSI devices does not fully emulate the SCSI interface. Further, this configuration is complicated, and its use with high availability versions of virtual tape server or VTS has been difficult. It would thus be desirable to allow an Open System host computer to attach to automated data library through a single SCSI attachment as if it were in effect using a true SCSI tape library.
It is therefore an object of the invention to provide a method and system for converting medium changer commands from a small computer system interface or SCSI bus to formats acceptable to automated tape library commands.
It is another object of the invention to provide a method and system for converting medium changer commands from an open system attached computer over a small computer system interface or SCSI bus to formats acceptable to data storage media from an automated data library.
It is still another object to provide a method and system for emulating a small computer system interface type memory device in an open system attached computer with data storage media from an automated data library under control of a library manager.
It is still another object to a method for emulating a small computer system interface type memory device in an open system attached computer with data storage media from an automated data library under control of a library manager.
The above and other objects are achieved as is now described. A method and system are provided that emulate a SCSI Medium Changer device in a host computer communicating with an automated data library over a small computer system interface or SCSI bus. The computer communicates with storage media of an automated data library under control of a library manager in the automated data library. According to the present invention medium changer commands are provided over the small computer system interface from the personal computer to a tape server of the automated data library. The medium changer commands are then mapped to commands compatible with the library manager of the automated data library and then provided to the library manager. The present invention thus allows an open system host to attach with a single SCSI attachment as if the host were using a true SCSI tape library. The present invention also allows open system attachment to tape controllers of multiple tape systems.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the preferred embodiment of the present invention, taken in conjunction with the appended claims and the accompanying drawings.
The above as well as additional objectives, features, and advantages of the present invention will become apparent in the following detailed written description.